The paper examines ontological presuppositions and epistemological branches of Peace and Conflict Studies. It describes the narrower use of the concepts‗ ontology ‘and‗ epistemology ‘as sub-branch and branch of philosophy respectively and later focus on their meanings in the context of particular areas of inquiry. It highlights the most basic of the core field definition and distinction issues in Peace and Conflict Studies—what peace is; the nature, causes, outbreak, and dynamics of conflict; and the means for resolving conflict and building sustainable peace. It presents and offers answers to key ontological questions: what exist, in what form do they exist, what are the conditions under which they exist, what is their relationships with other things that are said to exist regarding the field of Peace and Conflict Studies. Furthermore, the paper reviews ways of knowing, understanding, explaining and justifying the ontological presuppositions. Thus it discusses the three epistemological branches of Peace and Conflict Studies proposed by Johan Galtung—empirical peace studies, critical peace studies, and constructive peace studies—and their implications for values, empirical data and theory. In light of this epistemology, the author posits that values, followed by data, take preeminence in the applied Social Sciences field of Peace and Conflict Studies.